Multi boot windows 7, windows 10 and ubuntu 18.04

Hi all.

My question is "proactive" but I suppose it may help also many other people in the future.

I already use EasyBCD successfully (excellent software insofar!) to dual boot between windows 7 and windows 10 with no problems. I would like to add a third OS to my system (ubuntu 18.04) but I read on the internet about some people facing serious boot problem after installation (they could not boot either windows or ubuntu). I checked my windows 10 and windows 7 systems and both boot in BIOS legacy mode. I believe this is "good" as usually boot problems arise with windows in EFI mode. My questions are: has anyone already installed ubuntu 18.04 alongside windows 10 and windows 7 (both in legacy mode) successfully (i.e. 3 OS)? What is the best method to secure myself in case something could go wrong and not be able to boot at all? Obviously I don't want to mesh up my system with restore disks ets... I do have read the procedures how to prepare the ubuntu ISO boot USB disk, disable windows 10 from fast booting etc. and also what to do after installation to "deactivate linux grub booter" and replace it with windows MBR but this time giving me the third choice of ubuntu 18.04 as well. Thank you.